Calibrating means for a variable frequency oscillator



March 2l, 1961 A. H. MAclszEwsKl ETAL 2,976,494

CALIBRATING MEANS FOR A VARIABLE FREQUENCY OSCILLATOR` Original FiledMay 13, 1954 2 Sheets-Sheet 1 l J C TER .WN Qww A* A Q5 ,a W l@ |W\ LH lNmNM. MHO/ N MN EN www* W f ,wml R R @REFER @w EN N /ww HJdw 5 A @Nwwmwwmw @a i T- w 7W@ mmvn Tmtmifilm TNL 1 m .d VLTL ITL w M \\l/ @w1 mwWw IL\ l- I.. s.. vlif. l

March 21, 1961 A. H. MAclszEwsKl ETAL 2,976,494

CALIBRATING MEANS FOR A VARIABLE FREQUENCY OSCILLATOR Original Filed May13, 1954 2 Sheets-Sheet 2 Ll l y l I 'l l 2227@ 742mg 29m mlm@ J/Z ^2meCALIBRATING NIE-AN S FOR A VARIABLE FREQUENCY OSCILLATGR originalapplication May 1s, 1954, ser. No. 429,547,

now Patent No. 2,881,315, dated Apr. 7, 1959. Divided and thisapplication Apr. 21, 1958, Ser. No. 729,742

6 Claims. (Cl. 331-44) This invention relates to signal generators andcircuits therefor and particularly to calibrated signal generators andcircuits therefor useful in testing electronic equipment.

The apparatus of the present invention includes a rad-io frequencyoscillator whose frequency is continuously variable over a definiterange of nite extent. The frequency of this oscillator, which can becalled the variable oscillator, is checked and calibrated against theoutput of a calibration oscillator. The calibration oscillator operatesat a fixed predetermined frequency huch for example as two megacycles.The output of the calibration oscillator is amplified in such a manneras to generate harmonicsof the fundamental frequency of the calibrationoscillator so Ythat calibrated signals can be obtained at regularintervals throughout the frequency range of the Variable oscillator.

In commercial devices it is desirable to `have calibration signalsavailable at one megacycle interval at least in the lower half of thefrequency range of the variable oscillator. Greater stability andaccuracy of the calibration signals are obtained if the fundamentalfrequency of the calibration oscillator is some multiple of onemegacycle.

Accordingly, it is an important object of the present invention toprovide a system wherein, for example, one megacycle calibration signalscan be produced when, for example, two megacycle fundamental referencefrequency is generated by the calibration oscillator whereby a smallernumber of harmonics of the fundamental reference frequencymay be used toachieve a given range of calibration.

- In connection with the foregoing object it is still another object toprovide a system of the type set forth in which calibration signals areobtained at one megacycle intervals in the lower halfrof thepredetermined frequency range of the variable oscillator and the spacebetween calibration signals in the upper half of the range of thevariable oscillator is two vmegacycles thereby giving a greater spreadbetween the calibration signals at the upper end of the frequencyspectrum where small movements of the calibrating dials effectrelatively large changes in frequency. v

These and other objects and advantages of the invention are achieved bythe signal generator illustrated in the accompanying drawings. In thedrawings wherein like reference numerals.have been used to designatelike parts throughout:

Fig. l is a circuit diagram, part diagrammatic, of the variable radiofrequency oscillator of this invention and its connection with thereactor tube, the calibration oscillator, and the radio frequency outputattenuator;

Fig. 2 is a simplified circuit diagram of the temperature compensatingcircuit for stabilizing the frequency of the variable radio frequencyoscillator; v

Fig. 3 is a block diagram illustrating the calibration system forcalibrating the variable radio frequency os- --Unid ,StatesPaten-tgillator by means of the calibration oscillator shown in igpl;

Fig. 4 is a chart showing the distribution of the frequencies of thespectral lines resulting from harmonic amplification of the fundamentalfrequency at which the calibration oscillator operates and illustratingthe fact that the spectrum is suppressed above a frequency, F, whichdesignates the upper limit of the range of operation of the Variableradio frequency oscillator;

Fig. 5 is a chart illustrating the frequencies at which calibration beatnulls are obtained within the frequency range of the variable oscillatorwhen the output of the variable oscillator is beat against the output ofthe harmonic amplifier of the calibrated oscillator; and

Fig. 6 is a chart illustrating the manner in which calibrated beat nullsare obtained at odd megacycle positions in the lower half of thefrequency range of the variable oscillator and why no calibarted beatnulls are obtained in the upper half of the range of the variable radiofrequency oscillator.

Referring now to the drawings and particularly to Fig. 1 there is shownthe calibrated radio frequency sect-ion of the signal generator madeaccording to and incorporating the principles of the present invention.The calibrated radio frequency section of the signal generator comprisesgenerally a calibrating oscillator 20, a harmonic generator andamplifier 22, a variable radio frequency oscillator 24 and a modulatingor reactor tube circuit 26. ln general the purpose of the calibratingoscillator 20 is to generate an accurate radio frequency operating at agiven fundamental frequency such as, for example, two megacycles, thisfrequency being calibrated and controlled to a high degree of accuracy.The output of the calibrating oscillator 20 isthen fed to the harmonicgenerator and amplifier 22 which generates harmonics of the fundamentalfrequency of two megacycles and amplifiers these harmonic frequencies aswell as the fundamental frequencyy to provide calibrating referencesignals.

The oscillator 24 is continually Variable over a specilied range and asillustrated has ve separate ranges over which the frequency iscontinually variable. vIt is oscillator 24 which will provide theworking signal to be used in testing and calibrating other electronicequipment. The output of the variable radio frequency oscillator 24 andthe output of the harmonic amplifier 22 are each fed' to the reactortube circuit 26 and there beat against each other. The output of thereactor tube circuit v26 is fed to a deviation meter or to a speaker sothat the difference between the variable oscillatorY frequency and theappropriate calibrating signal can be detected and adjusted to zero atwhich time the frequency of the variable oscillator 24 can be said to becalibrated.

Each element of the above radio frequency generating and calibratingcircuit will now be discussed in detail. Y Referring first to thecalibrating oscillator 20, this oscillator includes a duo-triode 28whose operation is controlled by a crystal 30. Although any suitablefrequency of crystal 30 may be utilized, a crystal operating at afrequency of two megacycles is preferred. A crystal operating at twomegacycles permits one megacycle beat nulls to be generated with the useof a minimum of harmonies of the fundamental operating frequency ofcrystal 30 as will be explained in full hereinafter. One of theterminals of crystal 30 is connected through a lead 32 to one of thecathodes 34 of tube 28 which is preferably a type 12AU7, and through aresistor 36 (820 ohms) to ground. The other terminal of crystal 3l) isconnected through a resistor 38 (820 ohms) to ground and through aresistor 40 (820 ohms) to the other cathode 42 of tube 28. The cathodes34 and 42 are heated by heaters 44 that are supplied with suitable poweraraeea' i through line 46. One of the control grids 48 is grounded andthe other control grid S is connected through a resistor '52 (4700 ohms)to ground and through a capacitor 54 (470 auf.) to one of the plates 56of tube 28. The other plate S of tube 28 is connected through a line 60,an inductance 62 (0.9 uh.) and a shielded inductance 64 (0.9 ph.) to asource 66 of high operating potential. A capacitor 63 (5000 auf.)isconnected from plate 58 to ground to filter out and prevent radioVfrequency oscillations from entering the power supply 66. Plate `56 isconnected through a variable inductance 76 and a resistor 72 (1000 ohms)to line 6@ whereby to provide a source of high operating potential forplate 56. There is provided in parallel with inductor 70 a capacitor 74(150 auf.) and the junction between inductance lirand resistor V"i2 isconnected to ground by another capacitor 76 (5000 auf) The abovedescribed circuit operates as a radio frequency oscillator at twomegacycles when inductor 7) is properly adjusted to produce a resonantcircuit at two rnegacycles.

The output from the calibration oscillator 2? is fed through a couplingcapacitor "I8 (470 puf.) from plate 56 to the rst grid of a tube 66which serves as the harmonic generator and amplifier for circuit 22.Tube 80 is preferably a pentode and may be for example a GAE-i6 or anyother pentode having similar'` characteristics. is' developed acrossresistor S2 connected from the grid to ground, this resistor having avalue of 47000 ohms. The third or suppressor grid of tube S0 isconnected di- -rectlyto vthe cathode and the cathode is provided withself bias through a resistor 34 (220 ohms) which is connected to groundand which has in parallel therewith a capacitor 86v (5000 ppt). Thesecond or screen grid is connected through a resistor SS (47000 ohms) toa source of operating potential through inductorsV 62 and 64 and isby-passed to ground by a capacitor 90 (5000 ppi). The plate of tube Stilis connected through a resistor 92 in series with an inductor 94 whichin turn is connected to a source of operating potential through aninductance 62 and 64. Resistor 92 preferably lhas a value of 400 ohmsand inductor 94 is so chosen that the amplifier 92 has a by-pass fromtwo megacycles` to and through 28 megacycles but has a relatively sharpcutotf betweenA 28 megacycles. and 30 rnegacycles. This is assuming thatthe operating range of the variable frequency oscillator 2.4 is tobe inthe` range from zero megacycles 'up to and including 28 megacycles. Itvthe' range of. the variable frequency oscillator 26 is to be greater or.less, the values of resistor 92 andV inductor l9 5 are chosenaccordingly. `The sharp cut-ott characteristics of these circuitVelements serve Va `purpose which will be more fully described later inthis specification when discussing thecalibration of oscillatorl 24. l p

The output from amplier 22 will consist of an accurately controlledsignal at two megacycles and the harmonics thereof up to and through the14th harmonic which corresponds to 28 rnegacycles. The 15th harmonic andhigher harmonics will be suppressed for reasons which will be moreapparent hereinafter.- The outf put of the amplilier 22 is fed through apair of series coupling capacitors' 96Y (10 auf.) and 98 (1 wtf.) to theplate of the tube in reactor circuit 26.

All of the operating potential for the tubes 28 and 80 and for the tubesin the oscillator circuit 24 and the reactor circuit 26 are suppliedfrom the power supply or source generally designated by the numeral 66.The power supplied to powersupply 66 is the usual 110 volts 60 cycleA.C. current which is supplied through a pair of lines 100 which will behereafter referred to as the main supply line. The power supply 66,which is illustrated diagrammatically in Fig. 1, includes suitabletransf formers and rectiiers. One of the outputs of the power supply 6 6is anon-regulatedV 6.3v volt heater supply, the

The input signal on the control grid of tubestit) connected to eachother.

terminals of which are indicated by the numerals "X and Y and are thesource of current for the cathode heaters described above. to anunregulatedvoltage point within power supply 66 for Supplyingvrelatively high Operating potentials, t0 the plates and grids of tubes28 and 8l). Another output from power supply 66 is a 6.7 volt heatersupply 101 which is used to heat the iilarnents of the tubes inoscillator circuit 24 and reactor circuit 26.

One of the principal outputs ofv power supply 66 is an unregulatedvoltage appearing on line 102. Line102 is connected to a resistor 104V(1600 ohms) whichv is in turn connected to a variable resistance 106(.1000 ohins).

,The movable arm 108 on theA variable resistance k1 ()6 is connected tothe plate of a voltage regulator tube 110 which may be of the typedesignated 0A2. The voltage appearing on arm 108 serves as a regulatedvoltage supply for use on certain of the grids and the plates in thetubes of circuits 24 and 26.

The variable radio lfrequency oscillator 24 utilizes a duo-triode 112which may be ofthe type designated 616. The cathode of tube 112 isheated -by a lament 114 which is supplied with power from the lowvoltage supply 1101. The cathode is grounded; the two control grids areconnected to each other and the two plates are The grids are alsoconnected to ground through a resistor 116 (33000 ohms) and to alcapacitor network which forms one of the tuning elements of theoscillator tank. More speciiically, the grids are connected to acapacitor 118 (82 wtf.) which isA in turn connected -to a groundedvariable capacitor 120 (12A-77.6 MA1), to apair of variable capacitors122 and 124 (having a combined capacitance ofv 8.0 to'66.8 Mitt),avcapacitor 126 (2.1 ,lL/rf.) in parallel with capaci'- tors 122 and 124,and a two section capacitor 128 (2.1 to 5.3 mit. per section) which isin parallel with capacitor 126. The upper ends of capacitors 124 and 126and'128 are connected to each other and through a line 130 to oneterminal 132 of a variable inductance 134 which rkforms a portion of thetuned circuit of the oscillator V24. The oscillator circuit 24 has tiveseparate ranges and, accordingly, ive separate coils 134L havingidentical connections `but ditl'erent circuit values are provided.Thecenter terminal 136 of" coil 134 is connected through a line 138 to aYresistor 14A)l (47 ohms) which is in turn connected to a resistance 142 (400 ohms) in series withjaln inductance 144. Inductance 144 isconnected through a line 146, inductance 146 (Meh.) and inductance 150('14 uh.) -to the arm 108 on which appears the regulated high potentialypower supply.

The other terminal 152 of coil 134 is connected through a line 154 tothe plate of tube 112 and: accord.- ingly the plate oftube 112 receives,D.C potential through the coilk 134. The plate of tube 1!12` is alsoconnected to ground through a series ofV three parallel capacitors,namely a variable capacitor 156 (1.7-8.7 ppi), axed capacitor 158 (10hat.) and another variable capacitor 160 V(9.2--17-2 ppi).

Capacitors 126, 121 and 160 are ganged together. `'l'lhe describedcircuit |24 is operable to produce a con tinually variable frequencyover a given range, there being several different individual ranges.More particularly each coil 134 is adjustable to provide a continuallyvarying frequency over a given specified range for the particular coil134.

The output from the variable oscillator 2 4 is taken from the platethrough a lline 162 to the plate of a tube 164 in the reactor circuit26. Tube 1 64 is pretjerably a (SAI-I6 pentode.

The cathode of tube 164 is heated by, a filament 166 which is suppliedwith potentialy from the low voltage filament supply line 101. The thirdgrid of the tube is connected directly tothe cathode. and thev cathodeis in turn connected to` ground through a resistance 16S The inductor 64is connected- (t100 ohms). Cathode bias is provided for tube 164 byproviding resistance 168 with a by-pass Capacitor 170 (800 ppi).

The control grid of tube 164 is connected through a Capacitor 172 (10auf.) to the plate of tube 164 and to the plate of tube 112 in thevariable oscillator. The control grid of tube 164 is also connected to asuitable RL Circuit generally designated by the numeral 174 which Eis inturn connected to-a resistor 176 (470 ohms). Resistor '176 is connectedto an inductance 178 (14 uh.) vand an inductance 180 (14 ph.) to akilocycle deviation meter when Calibrating and to a source of AFmodulating voltage when desired. One end of resistance 176 is connectedto ground through a capacitance 182 (470 Mi)- y Instead of the RLcircuit 174, an RL circuit 174A, a resistance 174B, a resistance 174C,and a RC circuit 174D are provided yfor use on difference frequencyranges. The various circuit elements 174-174D are `ganged to the coils134-134D so that these elements are automatically switched in bothcircuits when the frequency of oscillator frequency circuit 124 -ischanged.

The variable frequency oscillator 24 when constructed as described abovehas in the output thereof a significant Content of the second harmonicof the fundamental fre- 'quency of the working signal which is useful inCalibrating the working signal at certain points, as will be described'more fully later. The reactor Circuit 26 is also in- '.herentlynonlinear in character and serves to emphasize and to generate thesecond harmonic of the working signal fed thereto from the variablefrequency oscillator '24. v The modulated or unmodulated output from thevariable oscillator 24 is fed to a piece of electronic equip- -mentto betested by means of an output radio frequency attenuator generallydesignated by the numeral `191 in Fig. l. The attenuator includes ingeneral a pick-up coil 192, one end of which is grounded as at 194 andthe other end 196 of which is connected to the electronic equipment tobe tested. Coil 192 is inductively coupled to the coil 134 in the tankcircuit 24. An electrostatic shield 198 is provided to preventexcitation of the pick-up loop or coil 192 by capacity Coupling. Thev'pick-up coil 192 is positioned within a metal tube 208 so that thetube and coil operate on the inductive-coupling mode as a wave -guidebelow Cutoff.

`A' pick-up loop or monitor wire 282 is provided, the

monitor wire extending into the tube 200 and being .positioned betweenthe pick-up loop 192 and theelectrostatic shield 198. The position ofmonitor loop- 202 is adjustable. A connection is made from the monitorloop 202 through a rectifier 204 ,a resistancey 206, an inductance 208and a second inductance 210 to a speaker. A capacitor 212 -by-passesresistance 286 to ground.

Referring now to Figs. 3 to 6- of the drawings, the new improvedcalibration system of the present invention will be described in detail.In Fig. 3 a block diagram is utilized to illustrate the fact that thecrystal Controlled oscillator 20 has its output fed to a harmonicgenerator and amplifier 22 which produces a plurality of calibrationsignals fs. In the example of Fig. l the fundamental frequency of thesignals fs is two megacycles and there is a signal at each two megacycleinterval up to` and including a 28 megacycle signal. All harmonics oftwo megacycles above 28 megacycles are suppressed by the Circuitelements 92 and 94 in Fig. l. These figures are ybased on the assumptionthat the output of the variable oscillator 24 is to be confined in therange of from zero to 28 megacycles. The output voltage, fv of thevariable oscillator 24 is therefore always at a frequency within therange of zero to 28 megacycles.

The two signals fs and fv are fed into the reactor 26 where they arebeat against each other and the difference frequency, which is an audiofrequency when f, and fv `generator and amplifier 22.

are lnearly identical, appears as a beat note in earphones,

has a component lat ,each/two megacycle interval beginning `vtith aftwomegacyclesignal up to and includingl a signalat ,281 megacycles. VAll`signalsabove 28 megacycles are suppressed. Y 1

The graph in Fig. 5 illustrates the points in the frequency spectrumfrom zero to 28 megacyclesk at which Calibrating beat nulls are obtainedwhen the output from generator 22, fs, is beat against the output fromthe variable oscillator 24, fv, in the mixer stage 26. It will be seenthat a Calibrating beat null is obtained at each one megacycle positionfrom zero through 14 megacycles and that a Calibratingv beat null isobtained at two megacycle intervals beginning With a frequency equal to14 megacycles. No beats appear above 28 megacycles.

The Calibrating beat nulls at the even numberedimega- ,Cycle position,that is at 2, 4, 6, 8 etC. megacycles are .obtained in the normal mannerby directly beating the `fundamental of the frequency, fv, against oneof the Calibrating signals -fs illustrated in Fig. 4.

By referring to Fig. 6 the manner in which Calibrating ,beat nulls areobtained at the odd numbered megacycle points, such as at one megacycle,3 megacycles, etc. in the range from one megacycle to 13 megacycles willbe explained. For example when the frequency fv equals 3 megacycles (thepoint indicated by the designation fvl Yin Fig. 6) the second harmonicof fvl, i.e., a 6 megacycle signal, is beat against the 6 megacycleCalibrating signal designated by the character fsl in Pig. 6. Thus bybeating the second harmonic of the variable oscillator signal against aCalibrating signal higher in the spectrum, Calibrating beat nulls can beobtained at the odd megacycle positions. By way of further illustration,a signal fvg having a value of 9 megacycles which is generated by' thevariable oscillator 24 will produce a Calibrating beat null by beatingthe second harmonic thereof of 18 megacycles against the Calibratingsignal fsz at 18 megacycles.

The above described method of obtainedl Calibrating beat signals at theodd numbered megacycle positions is effective up to and including asignal at 13 megacycles. There is no Calibrating beatsignal at 15megacycles or higherodd numbered megacycle positions since theCalibrating signals fs are suppressed above the frequency, F, or 28megacycles. lf it is attempted to obtain a Calibrating beat null at forexample fva equals 2l megacycles, no beat null would be achieved sincethe second harmonic of fva is 42 megacycles and there is no Calibratingsignal fs at 42 megacycles against which to beat this second har monicof the variable oscillator output. It will be seen therefore that therewill be no Calibrating beat nulls at the odd numbered megacyclepositions above 14 mega- Cycles.

The above Calibrating arrangement has an important advantage sinceordinary Calibrating beat nulls are desirable at one megacycle intervalsonly at the low end of the spectrum. At the higher end of the spectrumit is actually a disadvantage to have Calibrating signals at onemegacycle intervals since the Calibrating signals occur too frequentlywith. a given Change in setting of the dials Controlling the output ofthe variableoscillator 24. In effect a spread in the Calibrating signalsis obtained in the upper half of the frequency spectrum from F/2 to Fthus simplifying Calibrating in this range and yet retaining onemegacycle Calibrating signals in the lower half of the range where thereis a greater spread on the calibrating dials.

This application is a division of the copending` applicatioriSerial No.429,547, led May 13, 1954 for Multi- Band Compensated Oscillator, nowPatent No. 2,881,315 issued April 7, 1959. Y It will be seen that therehas been provided a signal generator fulfilling al1 of the yadvantagesand objects set forth above. Although certain speciiie examples andvalues of the circuit elements have been givenfor purposes ofvillustration, itis to be understood that various changes can bemade'therein without'departing from the spirit and scopeof theinvention. Accordingly, the invention is to be limited only as set forth'in the following claims.

` lWhat is claimed is:

1,. The method -of calibrating the frequency of the working signalgenerated Vas the output from a variable frequency oscillator within apredetermined frequency range at first predetermined accuratefrequencies equally spaced throughout the predetermined frequency rangeand at second predetermined accurate frequencies at the mid-pointsbetween the first 'predetermined frequencies only in the lower half ofthe predetermined' frequency range, comprising generating a first signalhaving an accurate fundamental frequency corresponding to the intervalbetween the first predetermined frequencies, generating harmonics of thefirst signal within the predetermined frequency range and suppressingall harmonics outside of the predetermined frequency range to provide aplurality of equally spaced calibrating signals at the `firstpredetermined frequencies, operating the variable frequency oscillatorto obtain as an output therefrom a obtainV the second harmonic of theworking signal fundamental frequency, the working signal fundamentalyfrequency during calibration Kbeing approximately the frequency of oneof the first and second predetermined frequencies, beatingthefundamentalfrequency of` the working signal4v from the variable frequencyoscillator "against the'calibrating signal having the frequency ltowhich the working signal is to be adjusted when calibrating the variablefrequency oscillator at one of the first predetermined frequencies andadjusting the frequency of the working signal until it produces a beatnull with the appropriate calibrating signal, and beating the secondharmonic of the working signal from the variable frequency oscillatoragainst the Calibrating signal having twice the frequency to which theworking signal is to be adjusted when calibrating they variablefrequency oscillator at one of the second predetermined frequencies andadjusting the frequency of the working signal until the second harmonicthereof produces a 'beat null with the,

vwithin the predetermined frequency range and suppressing all harmonicsabove the predetermined frequency range to provide a plurality ofcalibrating signals at two megacyle intervals, operating the variablefrequency oscillator to obtain as one output therefrom having a desiredfundamental frequency within the predetermined frequency range andalsoto obtain the second harmonic ofthek working signal fundamentalfrequency, the working signal fundamental frequency during 'Calibratingbeing approximately the frequency of one of the first and secondpredetermined frequencies, beating the fundamental frequency of theworking signal from the variable frequency oscillator againstqtheVCalibrating signal havingthe frequency to which the working signal is tobe adjusted when Calibrating the variable frequency oscillator atone ofthe first predetermined frequencies and adjusting the frequency of theworking signal until it produces a beat null with the appropriateCalibrating signal, and beating the second harmonic of the workingAsignal from the variable frequency oscillator against the calibratingsignal having twice the frequency to which the working signal is to beadjusted when calibrating the variable frequency oscillator at one ofthe second predetermined frequencies and adjusting the frequency of theworking signal until the second harmonic thereof produces a beat nullwith the appropriate Calibrating signal. v

3. In frequency Calibrating apparatus for Calibrating the frequency ofthe working signal generated as the output from a variable frequencyoscillator within a prede- 2working signal having a desired fundamentalfrequency 'within the predetermined frequency range and also to terminedfrequency range at first predetermined accurate frequencies throughoutthe predetermined frequency .range and at second predetermined accuratefrequencies at the mid-points between the iirst predeterminedfrequencies only in the lower half of the predetermined frequency range,wherein' the variable frequency oscillator is operable to provide asthek output therefrom the working. signal at a desired fundamentalfrequency and, the second harmonic thereof, comprising a Calibratingoscillator operable to produce a first signal having an accuratelycontrolledfundamental frequency corresponding to the interval between`the.l firstA predeterminedl frequencies, an harmonic generator andamplifier for generating harmonies of the first signal within thepredetermined'frequency range, means for suppressing all harmonics ofthe first signal outside of the predetermined frequencyrange to provideequally spaced Calibrating signals throughout `the predeterminedfrequency range,` a mixer for beating the working signal and the secondharmonic thereoffrom the variable frequency oscillator against theappropriate 'Calibrating signal, said mixer beating the fundamentalfrequency of the working signal from the variable frequecy oscillatoragainst the Calibrating signal having the frequency to which the workingsignal is to be adjusted, when 'calibrating the variable frequencyoscillator at one of; the

first predetermined frequencies, said mixer beating the second harmonicof the working signal froml the variable frequency oscillator againstthe-calibrating signal having twice the frequency to which the workingsignal is to be adjusted when Calibrating the variable frequencyoscillator at oneof the second predetermined frequencies,-and means fordetecting the beat null when the working signal and the second harmonicthereof are properly adjustedto and beat against the appropriatecalibrating signal.

, 4. In frequency calibrating apparatus for Calibrating the frequency ofthe working signal generated as the output from a variable frequencyoscillator within a predetermined frequency range at iirst predeterminedaccurate frequencies spaced at two megacycle intervals throughout thepredetermined frequency range and at second predetermined accuratefrequencies at the mid-points between the first predeterminedfrequencies only in the lower half of the predetermined frequency range,wherein the variable frequency oscillator is operable to provide as theoutput therefrom a working signal at a desirable fundamental frequencyand the said harmonic thereof, comprising an oscillator operable toproduce a first signal having an accurate fundamental frequency of twomegacycles, an harmonic generator and amplifier for generating harmonicsof the first signal within the predetermined frequency' range, means forsuppressing all harmonics of the first signal above thepredeterminedfrequencq range to provide CalibratingV signals at twomegacycle intervals throughout the predetermined frequency range, amixer for beating the working signal and the second harmonic thereoffrom the variable frequency oscillator against the appropriatecalibrating signal, said mixer beating the fundamental frequency of theworking signal from the variable frequency oscillator against thecalibrating signal having the frequency to which the Working signal isto be adjusted when calibrating the variable frequency oscillator at oneof the first predetermined frequencies, said mixer beating the secondharmonic of the working signal rom the variable frequency oscillatoragainst the calibrating signal having twice the frequency to which theworking signal is to be adjusted when calibrating the variable frequencyoscillator at one of the second predetermined frequencies, and means fordetecting the beat null when the working signal and the second harmonicthereof are properly adjusted to and beat against the appropriatecalibrating signal.

5. Apparatus for providing a calibrated working signal accuratelycalibrated within a predetermined frequency range at first predeterminedaccurate frequencies throughout the predetermined frequency range and atsecond predetermined accurate frequencies at the mid-points between thefirst predetermined frequencies only in the lower half of thepredetermined frequency range, com` prising a variable frequencyoscillator operable to provide as the second output therefrom a worln'ngsignal at a desirable fundamental frequency and the second harmonicthereof, a calibrating oscillator operable to produce a first signalhaving an accurate fundamental frequency corresponding to the intervalbetween the first predetermined frequencies, an harmonic generator andamplifier for generating harmonics of the first signal within thepredetermined frequency range, means for suppressing all harmonics ofthe first signal outside of the predetermined frequency range to provideequally spaced calibrating signals throughout the predeterminedfrequency range, a mixer for beating the working signal and the secondharmonic thereof from the variable frequency oscillator against theappropriate calibrating signal, said mixer beating the fundamentalfrequency of the working signal from the variable frequency oscillatoragainst the calibrating signals throughout the predetermined frequencying signal is to be adjusted when calibrating the variable oscillator atone of the first predetermined frequencies, said mixer beating thesecond harmonic of the working signal from the variable frequencyoscillator against the calibrating signal having twice the frequency towhich the working signal is to be adjusted when calibrating the variablefrequency oscillator at one of the second predetermined frequencies, andmeans for detecting the beat null when the working signal and the secondharmonic thereof are properly adjusted to and beat against theappropriate calibrating signal.

6. Apparatus for providing a calibrating working signal accuratelycalibrated Within a predetermined frequency range at rst predeterminedaccurate frequencies accurately spaced at two megacycle intravalsthroughout the predetermined frequency range and at second predeterminedaccurate frequencies at the mid-points between the first predeterminedfrequencies only in the lower half of the predetermined frequency range,comprising a variable frequency oscillator operable to provide as theoutput therefrom a working signal at a desired fundamental frequency andthe second harmonic thereof, a calibrating oscillator operable toproduce a -rst signal having an accurately controlled fundamentalfrequency of two megacycles, an harmonic generator and amplifier forgenerating harmonics of the fundamental frequency of the iirst signalwithin the predetermined frequency range, means for suppressing allharmonics of the first signal outside of the predetermined frequencyrange to provide equally spaced calibrating signals at two megacycleintervals throughout the predetermined frequency range, a lmixer forbeating the working signal and the second harmonic thereof from thevariable frequency oscillator against the appropriate calibratingsignal, said mixer beating the fundamental frequency of the workingsignal from the variable frequency oscillator against the calibratingsignal having the frequency to which the Working signal is to beadjusted when calibrating the variable frequency oscillator at one ofthe first predetermined frequencies, said mixer beating the secondharmonic of the working signal from the variable frequency oscillatoragainst the calibrating signal having twice the frequency to which theworking signal is to be adjusted when calibrating the variable frequencyoscillator at one of the second predetermined frequencies, and means fordetecting the beat null when the working signal and the second harmonicthereof are properly adjusted to and beat against the appropriatecalibrating signal.

References Cited in the le of this patent UNITED STATES PATENTS2,508,547 Slonczews-ki May 23, 1950 2,629,829 Daly Feb. Z4, 19532,686,294 Hower Aug. 10, 1954 2,738,462 Troxel Mar. 13, 1956 UNITEDSTATES PATENT oFFIoE CERHFICAHON @F @DEBE-GRN Patent No@ 214976U494Manch 2l? 1961 Arthur Ho Meciezewski et el.

It s l'l'ef'eby certified that e'ror appears n the above numberedpate111'J requiring eorzecton and 'that the said Letters Patent shouldread as corrected below. e

Column l.J line 25l for mllnucln reed m such mm; column. 2iJ line 37Yfor "'ampliiiers" read m amplifies @m3 Column 5U line 49g for"theelecrom" read m the elf-)ciuffon mg celumn 9uy lines l2 and 43@ forsignals throughout, the predeiermined negueney ing signal read w signalhaving the frequency to which the working signal column l()7 line L7 for"'intravalsf read ma intervals ma,

Signed and sealed this 5th day of September lQL SEAL Atgest:

ERNEST W. SWIDER DVD L. LADD Attesting Officer Commissioner of Patents

